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Prophecy variables with lists

Merged Rodolphe Lepigre requested to merge lepigre/iris:prophecy_list into master

We generalize the prophecy variable mechanism so that prophecy variables can be resolved several times. A prophecy variable is hence associated to a list of values. This means that several "observations" can be made for a given prophecy variables, but the overall intuition remains the same. The main difference is in the specification of the resolve operation:

Lemma wp_resolve_proph (p : proph_id) (vs : list val) (v : val) :
  {{{ proph p vs }}}
    ResolveProph (Val $ LitV $ LitProphecy p) (Val v)
  {{{ vs', RET (LitV LitUnit); ⌜vs = v::vs'⌝ ∗ proph p vs' }}}.

Note that resolving p consumes only the first of the list vs, and the ownership of proph p vs' (where vs' is the tail of vs) is asserted in the postcondition.

In any case, everything remains very simple, and even simpler than before. The main difference being that we replace an option by a list.

@jung do you have anything to add?

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